1. Field of the Invention
The present invention relates to a magnetic head, and particularly to a magnetic head including a microstripline for writing information to a recording medium by using a microwave assisted magnetic recording system.
2. Description of the Related Art
In recent years, high recording density has been demanded in hard disk drives (HDD), and a perpendicular magnetic recording system has been used as the recording system therefor. In the perpendicular magnetic recording system, a magnetic domain size is reduced, and high recording density is realized by making the magnetization direction of a recording bit (magnetic domain) perpendicular to a recording medium.
In general, when a magnetic domain is miniaturized, a heat stability problem of recording magnetization occurs in conjunction with the volume reduction of magnetic microparticles that form the recording medium. In other words, there is a risk of loosing information that is recorded on the recording medium due to so-called “heat fluctuation” of magnetization. This is much the same in the perpendicular magnetic recording system. As a method to solve the heat stability problem, use of a material that has a large magnetic anisotropy for the recording medium can be considered. In that case, an extremely large recording magnetic field (writing magnetic field) by the magnetic head is required to perform magnetization reversal in order to write information to the recording medium.
In the perpendicular magnetic recording system, a magnetic head known as a single magnetic pole type is used. As for this type of magnetic head, there is a demand for narrowing the width of a magnetic pole layer that generates a recording magnetic field in correspondence with the high recording density (narrowing the track width) of the recording medium. However, since narrowing the magnetic pole width leads to a reduction of the generated recording magnetic field, it is not preferable for the recording medium that requires an extremely large recording magnetic field as described above.
In contrast, a recording system, which is referred to as a microwave assisted magnetic recording system, is proposed that enables magnetization reversal with a weak recording magnetic field. According to this recording system, it becomes possible to reduce the recording magnetic field necessary for magnetization reversal by applying a high frequency alternate-current (AC) magnetic field (hereinafter, referred to as the “assisting magnetic field”) in an in-plane direction of the recording medium simultaneously with the recording magnetic field. The frequency of the assisting magnetic field applied at that time is the frequency (between several GHz and 10 GHz) of the microwave band that corresponds to the ferromagnetic resonant frequency of the recording medium.
There is a method using a microstripline as one method to generate the assisting magnetic field. For example, Japanese Laid-Open Patent Application No. 2009-80869 discloses a magnetic head with a microwave path (microstripline) in the vicinity of a magnetic pole that generates a perpendicular magnetic field (writing magnetic field). In this magnetic head, a portion of the microstripline is formed so as to face the recording medium. A high frequency current is applied to the microstripline, and thereby, an AC magnetic field generated in a region of the microstripline that faces the recording medium is used as the assisting magnetic field.
In the microwave assisted magnetic recording system, there is a demand for further improvement in recording density by concentrating the assisting magnetic field in a more minute region. To accomplish this, the region that generates the assisting magnetic field must be formed narrowly in the method in which the above-described microstripline is used. However, from a perspective of processing technology, there is a limit to narrowly forming the microstripline itself. Further, the ability to apply a large assisting magnetic field to the recording medium allows a material having a large magnetic anisotropy to be used as the recording medium. However, in the method described above, even if the microstripline could be formed in a desired shape, it would require an extremely large undesirable current to generate the assisting magnetic field at a level of several kOe.